Microstructure and mechanical properties of as-cast Mg-8Sn-1Al-1Zn-xNi alloys

Mg-8Sn-1Al-1Zn-xNi (x=0.5%, 1.0%, 1.5%, 2.0%, mass fraction) alloys were designed and prepared. The microstructures and the mechanical properties were studied by using optical microscope, scanning electronic microscope, energy dispersive X-ray spectroscope, X-ray diffraction and a standard universal testing machine. The results show that the microstructure of Ni-containing alloys consist of alpha-Mg, Mg2Sn, beta-Mg-Ni-Al and gamma-AlNi phases. No beta-Mg-Ni-Al phase was observed in TAZ811-2.0Ni alloy due to its 1:1 atomic ratio of Ni/Al. The addition of Ni refines the alpha-Mg dendrites and suppresses the formation of coarse Mg2Sn phase. The tensile properties results show that the TAZ811-0.5Ni alloy presented the best mechanical properties, which is due to the rod-like beta-Mg-Ni-Al phase, refined alpha-Mg dendrites and Mg2Sn phase, as well as gamma-AlNi phase. The tensile fracture mechanism transits from cleavage to quasi-cleavage fracture with the increasing Ni addition.